Funky Genetics: Baby is Born to Three Parents
On Tuesday, April 11, a baby was born to three parents.
I’m sorry, pardon?
It’s true. Scientists went there. Actually, this wasn’t even the first time. However, it was the first time that this particular technique was used for a new application — treating infertility. What happened?
The story starts in the mitochondria, the organelle responsible for cellular respiration in Eukaryotic cells (not Bacteria or Archaea). Eukaryotic cells have very specific traits; importantly, they contain a nucleus within which resides the linear DNA of the cell. Bacteria, on the other hand, have no nucleus. Rather, their circular DNA floats freely throughout the cytoplasm. In a similar fashion to chloroplasts, in which photosynthesis occurs in plants, the mitochondrion is a unique organelle. Both chloroplasts and mitochondria contain their own unique set of DNA that is located throughout the area in each organelle that is analogous to the cytoplasm — the mitochondrial matrix or chloroplast stroma. This is one of the clues suggesting that the mitochondria and chloroplasts used to be free-living prokaryotes who were absorbed at some point by other cells to eventually become codependent on each other. This is also the scientific basis for why the heck this baby has three parents.
Mitochondrial DNA (mtDNA) is still DNA, if a little different from the rest of our DNA. This means it can be inherited from parents/passed down to children. It also means that mitochondria can carry their own genetic disorders. Interestingly enough, mtDNA is only inherited from the mother, not the father. So, if the father has a mitochondrial disorder from a mutation in mtDNA, there is no chance of the child inheriting the disorder. However, if the mother has one, then the child will inherit the mutation. The child may not inherit the mutation in the same way as the mother, though, since maternal mtDNA gets distributed randomly into the embryo. According to this article from the New York Times, it can be like playing Russian roulette. The baby might end up inheriting the mtDNA in such a way that he/she is perfectly healthy. Or, they may develop a disorder that ends up being fatal.
As scientists have been messing around with DNA in the area of genetic engineering, they have also come up with a particular technique to prevent disorder-causing mtDNA from being passed along to children. There are two ways to go about this, but both have the same core concept: an egg is taken from the mother with the mtDNA mutation, an egg is taken from a woman with average mtDNA, and the nuclei are swapped before in vitro fertilization is performed. The method used in this case is called maternal spindle transfer (MST), while the other method is called pronuclear transfer. If the IVF is successful, the resulting child will still be able to develop a mutation leading to a mitochondrial disease on their own (mitochondrial diseases can occur from mutations in genes from regular DNA that code for mitochondrial proteins, or from random mutations). Nevertheless, the child will not inherit the mutation from the mother.
This technology is important for those who want children, but who risk passing on a mitochondrial disorder. So, yeah, MST could theoretically be a way to essentially eradicate inherited mtDNA disorders, assuming that anyone who has a mutation has access to and can afford the procedure (considering the steep costs of IVF, it’s safe to say that mitochondrial donation isn’t going to be the cheapest way to conceive).
This wasn’t the first time that this technique has happened. In fact, the first baby to be born using a similar method (albeit not quite the same) was born in 1997. Later, in 2017, MST successfully gave a healthy child to an Israeli family in Mexico. Interestingly enough, this technique has another application — the mother of the baby born this week didn’t have a mitochondrial disorder. Rather, the parents underwent MST in order to treat infertility, and it worked! This is the first time that MST has successfully given a child to parents dealing with infertility. This groundbreaking achievement has further confirmed what fertility doctors and scientists have known for a while now — that the health and ‘quality’ of maternal mitochondria are related to fertility and reproduction. Exactly what effect the mitochondria have on fertility is still up for discussion, but there is definitely a link and, in some cases, infertility may be overcome using MST.
MST is front and centre in many discussions on the ethics of genetic engineering. Some worry that this may be indicative of another step closer to giving parents the ability to pick and choose their child’s genetics — not unlike the ‘Create-a-Sim’ page that many gamers are familiar with. Good news: this method really doesn’t allow for much choice in the matter of what genes the child will inherit. Genes for height, hair colour, skin colour, and other superficial traits are all encoded in nuclear DNA, which is not edited at all in MST. Going back to the endosymbiotic theory, the mtDNA is derived from bacterial DNA and is therefore unrelated to any traits that eugenicists would be looking for. mtDNA simply contains genetic information related to the mitochondria. The only change that can be made is swapping harmful mtDNA with non-harmful mtDNA. That being said, there are some other ethical issues, as well as legal. Only time and research will tell what other dangers there are to this form of IVF. For now, though, it seems to be a really positive thing. I mean, science can give children to mothers with mitochondrial disorders and to infertile couples. That seems noble enough to me.
